Temperature compensator for dynamo-electric machines



Dec. 22, 1931. DAVIS ET AL 7 1,837,951

TEMPERATURE COMPENSATOR FOR DYNAMO ELECTRIC MACHINES Filed May 51, 1930 3 Sheets-Sheet l INVENTORS ATTORNEY Dec. 22, 1931.

L. l. DAVIS ET AL TEMPERATURE 'COMPENS'ATOR FOR DYNAMO ELECTRIC MACHINES Filed May 31, 1930 3 Sheets-Sheet 2 C cl 'cwca GENERATOR ELEVATOR MOTOR INVENTORS ATTOR NEY Dec. 22, 1931. DAVIS ET AL TEMPERATURE COMPENSATOR FOR DYNAMO ELECTRIC MACHINES Filed May 31, 1930 3 Sheets-Sheet 3 5 m T N E V W.

ATTORNEY Patented Dec. 22, 1931 UNITED STATES PATENT OFFICE LEE IRWIN DAVIS, OF NEW YORK,--AND DAVID CARL LARSON AND GEORGE WILLIAM LAUTRUP, OE YONKEBS, NEW YORK, ASSIGNOBS TO OTISELEVATOR COMPANY, 01 NEW YORK, N. Y.,.A CORPORATION OF NEW JERSEY TEMPERATC'RE COMPENSATOR FOR EYNAMO-ELECTRIC MACHINES Application filed la in,

The invention relates to control systems and especially to control systems for elevators.

As the art of elevators has developed, various improvements have greatly increased the efiiciency of operation of the elevator systems over those of the earliest types. Among these improvements have been those designed to reduce the time required to complete certain operations such as acceleratlng and retarding the cars'and stopping the same high speed elevator systems heat up to their maximum temperature in about four hours. A temperature rise of eighty degrees Fahrenheit causes an increase of approximately twenty per cent in the resistances of the windings. I

With a Ward Leonard system of control in which a direct current driving motor is employed, the resulting increase in speed is somewhat less in proportion than the increase in resistance, since as the generator field winding becomes heated its resistance increases, cuts down on the current flowing through said winding, weakens the generator field, and reduces the output voltage of the generator. This tends to reduce the elevator motor speed, thus partially compensating for the increased speed caused by the heating of the driving and elevator motor field windings. In spite of the partial compensation afforded by the heating of the generator field winding, the elevator speeds show an increase of ten per cent or more. This variation in speed has an undesirable effect on the control of the elevators.

It is important that the acceleration and re- 1930. Serial No. 457,765.

tardation'of the elevator cars be regulated in such a way that no time is lost, and also that the levelling, or correction distance at the landing, does not vary too much. It has been found, particularly after the electrical ap-. paratus has become heated, that quite long levelling cams are necessary, as otherwise,

the cars will stop outside the levelling zone and will not level at the landing. It is necessary not only to use. long cams for levelling but also to lengthen the time required for retarding the elevator by the main control, thus causing sluggish operation and loss of time, so thatthe elevators are not able to give the proper trafiic handling capacity.

The principal object of this invention is to remedy the above difficulties and insure uniform speed operation of elevators.

One feature of the invention is to obtain practically uniform speed from an electrical unit regardless of the heating of its field windings.

Another feature of the invention is to obtain practically uniform speed of the elevator car from a combination of electrical drive units regardless of the heating of their field windings by the control of the current flowing through one or more of said field windings.

Other features and advanta es will become apparent from the following escription and appended claims.

The invention involves the controlling of the current flowing through one or more of the field windings of an elevator driving unit by employing variable resistances electrically connected with the field windings of the unit and changing the resistances with respect to time.

The time required to change the variable resistances from their upper to lower limits is made the same as that required for. the field coils to become fully heated from a cold condition, and the resistances are made of ing position in the same time that it consumed to shunt the maximum resistance. It the elevator is again placed in service after. a short shut-down, the rheostat is st ed in the forward direction from a posi ion which it short-circuits nearly the same re sistance that it did at the time of shutdown. The rheostat action thus follows closely the heating and cooling of the field windings.

For the purpose of illustrating the genus of the invention typical concrete embodiments are shown in the accompanying drawings in connection with a Ward Leonard system of control.

Figure l is a diagram of an elevator control system embodying the invention;

Figure 2 is a diagrammatic representation oi? the control panel for the system illustrated in Figure 1 and showing the relation of the coils and contacts of various switches;

Figure 3 is a front elevational view of the motor driven rheostat shown diagrammatically in Figures 1 and 2,

Figure 4 is an end view of the device shown in Figure 3 with certain pats omitted;

Figure 5 is a fragmentary sectional view taken along the line 5 5 of Figure 3; and

Figure '3 is a diagrammatic view of a modified form of the invention applied to an alternating current drive.

l lo attempt is made in Figure 1 to show the coils and contacts of the various electromagnetic and other switches and associated parts intheir related positions, a straight dia-.

gram being employed wherein the coils, contactsand other parts are separated so as to render the circuits relatively simple. For a clearer understanding of the invention, the stationary contacts out the switches are illustrated in cross section.

The motor generator set employed comprises a driving motor 11, illustrated as of the direct current type, mechanically con nected to drive a variable voltage direct current generator -12. The armature of the driving motor is designated 13, its series field winding 14, and its separately excited field winding 15. The armature of thegenerator is designated 16, its series field winding 17, and its shunt field winding 18. The series field winding 17 may have any desired'numher of turns so as to efi'ect the proper compounding action of the generator. The elevator hoisting motor 1s designated as a whole by numeral 20, its armature being designated nearest 21, and its separately excited field winding 22. [a discharge resistance 23 is arranged in shunt with the generator separately excited field winding 18. Temperature compensating resistances 2d, 25 and 26 are arranged in. series with the separately excited field windings, of the driving motor, 22 of the elevator motor, and 13 of the generator, re-

spectively. Each of these resistances, 2d, and 26, is provided with a number of sta tionary contact blocks 27, numbered 1 to 10 inclusive, and is connected to said contact hloclzs by a desired number of selective taps 28 designates movable contacts engaging the contact blocks 27 to cut out such portions of each resistance as desired.

A. rheostat motor 29, having an armature 30, and reversing field windings 31 and 32, is provided for moving the contacts 23 to engage the several stationary contacts 27. The reversing field windings 31 and 32 are each provided with a discharge resistance 34 in shunt therewith. A resistance 33 is connected in series between the temperature compensating resistance 26 and the generator separately excited field winding 18. This single resistance 33, controlled in its action by accelerating switch coil F6 and a time relay reactance coil 36, illustrates only the last step of the accelerating means and may be indicative of any desired number of steps. 37 and 38 designate the direct current supply mains. M6 is the brake release coil for an electro-magnetic brake. This brake upon operation separates its back contacts M5 to insert a cooling resistance 40 in circuit with its coil M6. The car direction switch is designated as a whole by numeral 41. 12 is a safety switch in the car, and 43 and 4a are knife switches in the starting circuit. 45 designates a standing field resistance in the circuit for the elevator motor separately excited field winding 22 and its compensating resistance 25.

The electro-magnetic switches have been designated as follows:

i l-potential switch B-up direction switch Ii-clown direction switch li -accelerating switch G-maintaining relay l l-bralre switch l l starting switch Lfield control switch M-bralre release switch Rstarting relay X-minimum current field relay Y-rheostat limit switch Z-speed regulating switch Throughout the description which follows, these letters. in addition to the usual reference numerals, will be applied to the parts of theabove enumerated switches. For example, B are contacts on the up direction switch, While coil A, is the coil that operates the potential switch. The electro-magnetic switches are shown in their deenergized positions.

Referring to the starting operation of the driving motor, the start switch 44 is closed, completing the circuit through the coil R of starting relay R and through the knife switch 43. Relay R, upon operation, completes the circuit for coil K of the starting switch K by closing contacts R Switch K on closing its contacts K and K completes the circuit for the driving motor armature 13 and separately excited field winding 15, the contacts K and K being disposed one on each side of the line. These two contacts K and K of switch K also complete the circuit for the elevator motor separately excited field 'winding 22 through the coil X of the minimum current field relay, which coil X isshunted by contacts L of the field control switch L. At the same time, switch K, closes its contacts K to complete the circuit for the rheostat. motor 3 through rheostat limit switch contacts Y and reversing field winding 31, and opens its con- .tacts K to prevent the energization of the othera'eversing field winding 32 of this motor. Switch K, through contacts K also connects the coil L of the field control switch L across the driving motor armature. As the driving motor counter-E. M. F. builds up, switch L on closing contacts L operates to short-circuit the driving motor accelerating resistance, designated 39.

The elevator motor separately excited field winding 22 has a resistance 45 in circuit therewith. This resistance is of proper value to giv'ethe desired'strength of the elevator motor field with the car at a standstill, usually referred to as a standing field. The coil X bf the minimum current field' relay X, is also in series with the elevator motor separately. excited field winding 22. The contacts X}, of relay X, togetlier with the contacts L in circuit with the coil A of the potential switch A, and contacts L of switch L, in shunt to the coil X of relay X, act to prevent the Operation of the potential switch A and therefore cut off the supply of current to the generator field windings 17 and 18 until the driving motor 11 and generator 12 have come up to a certain speed and the elevator motor field has been built up to a certain value. This is to obviate runaway conditions when stopping-and starting the driving motor. Switch A upon operation closes its contacts A, and A to supply current to the generator field windings 17 and 18 and at the same time opens back contacts A to cut in a cooling resistance 19 in circuit with its coil A a The circuit for the potential switch A also passes through the safety switch 42 of the car and through the governor on the motor generator set, the contacts of said governor being designated 46. The purpose of the governor is to break the circuits for relay R time.

and switch A and K in the event of overspeed of the driving motor 11.

To-start the elevator car the car switch 41 is actuated to move contact bar 47 in a direction dependent upon the desired direction of car travel. Assuming up direction, contact bar 47. is moved so as to bridge contactsy48 and 49, completing the circuit for the up direction switch and brake switch coils B and H respectively, this circuit being through door contacts 51 and gate'contacts 52. Only one pair of door contacts 51 are shown as indicative of all the door contacts connected in series relation. B, upon operation, completes the circuit for the generator field by closing its contacts B and B Switch H, upon operation, completes. the circuit which energizesthe brake release coil M by closing contacts H shortcircuits, by closing contacts H the standing field resistance 45 in series with the elevator motor separately excited field winding 22, and gives a strong field for starting. Upon further movement of the contact bar 47 to engage contact 50, a circuit is established for Switch I the coil F 6 of the accelerating switch F, subject to the contacts H of switch H. The operation of switch F is delayed by the action tacts Z are opened by speed regulating switch Z, the coil Z of which is so connected as to be subject to the generator voltage.

Holding coils-B C, and H, are provided for the direction switches and brake switch. In starting the car in the up direction, the circuit for the holding coils B a-ndH of switches B and H is completed by contacts B of switch B and contacts F of switch F. As the generator field builds up, the current is sufliciently increased in its separately excited field winding 18 and in the coil G of maintaining relay G to cause theoperationpf the relay, thus closing the contacts G to bypass the contacts F -in .the above holding circuit. r

It is preferred further to provide the direction switches with a mechanical interlock to prevent their both being closed at the same Such an interlock may be in the form of a walking beam '55 pivotally mounted for engaging catches 56 and 57 onthe armatures voltage builds up to a certain value and coni of the direction switches as shown in Figure 2. Upon operation of the up direction switch in response to the energization of its actuating coil B contacts B B and B engage and contacts B separate breaking the circuit leading to the actuating coil C of the down direction switch.

To stop the car, the car switch 41 is re turned to off position. Switch F drops out immediately, reinserting resistance 33 in circuit with the generator field winding 18 and short-circuiting the temperature compensating resistance 25 which is in circuit with the elevator motor separately excited field winding 22. The rate at which the generator field strength decreases is controlled by the discharge resistance 23 connected in parallel with the generator shunt field winding 18 and consequently the rate at which the current in the coil G ot the maintaining relay Gr, which is in circuit with the field winding 18, decreases is similarly dependent. 'lihus, although accelerating switch F opens its contacts F in the above holding circuit for the direction switches and brake switch, this holding circuit is maintained established until relay G drops out and contacts G separate. The bralre switch and up direction switch are maintained in operated condition even though their operating coils are deenergized until the generator field strength has decreased to a certain value, and therefore until the generator voltage has decreased to a certain value. Upon the opening of the contacts G of the relay G, switches l3 and H are permitted to drop out effecting the deenergization of the generator field winding 18 and the application of the brake, thus bringing the car to a stop.

Contacts designated 53 of a safety governor.

switch (not shown) are arranged in parallel with the resistances 45 and 25, which are in circuit with the elevator motor separately e2;- cited field winding 22, to effect the shortcircuiting of these resistances in case of overspeed oi the elevator car. Also, additional contacts H are provided on the brake switch H for connecting the generator separately excited field winding 18 to the generator armature 16 upon the deenergization of said field winding. This is the usual suicide connection.

To stop the driving motor the start switch 44 is turned to ofi position, deenergizing the starting relay R and consequently deenergiz- -ing starting switch K. Switch K dropping out, not only breaks the circuit for the driving motor but also causes a. circuit to be completed for the rheostat motor 29 through its other reversing field winding 32 when contacts K separate and contacts K engage. This causes rotation of the rheostat motor in the opposite direction from that which occurred when the driving motor was started in operation. An adjustable resistance 54, in shunt to the rheostat motor armature 30, is provided for controlling the speed of this motor.

Referring particularly to Figures 3 and d, a motor driven rheostat embodies the compensating resistances and the stationary contact blocks 27 which are shown diagrammatically in Figure 1. The rheostat is preferably mounted on an insulating panel 60 and comprises a motor 29, a speed reduction gear box 62, and a multiple resistance unit 63. lhe motor 29 is operatively connected to the gear box 62 and both are secured to the panel 60 by bolts or. in order to secure the stationary contacts 27 to the panel 60 without interfering with the contact surfaces thereot holes are drilled in the bottoms of the contact blocks and studs 65 threaded into said holes. Studs 65 project through the panel 60 and are provided with securing nuts 68 to fasten the contact blocks to the panel and to provide terminals for suitable resistance elements 67 which comprise the compensating resistances. Each of the resistance elements 67 has a plurality of taps 35 to allow a selection of the desired values of resistance for a particular installation or to vary the rate at which resistance is short-circuited, which may be desirable under certain conditions. This selection of valves of resistance afiords the same control of the compensation of each drive unit that could be effected by supplying each compensating resistance with an independently driven rheostat having means for controlling its speed.

The stationary contact blocks 27 are an ranged in three parallel rows corresponding to rows of resistance elements 6-7 which make up each of the compensating resistances. it cross-head 68 carrying brush contacts 69 and a nut 70 is mounted so as to travel along the rows of stationary contacts. A screw 71 projecting from the reduction gear box 62 serves as the actuating and mounting means for the cross-head 68, said screw being threaded to the nut 70. A bearing member 72 bolted to the panel 60 is provided for the projecting end of screw 71. To the cross-head 68, there is secured substantially U-shaped support members 74, one leg of each being bolted to the cross-head and the other leg having an opening 75 therethrough and an inwardly directed forked end T6. The brush contact members 69, each having a normally disposed lug 78 at one end adapted to fit loosely the opening 7 5 and the other end curved to form a wiping contact portion 77 for engaging stationary contact blocks 27, are mounted in the support members 74;. The lugs 78 and body portions of the contact members 69 are biased into the openings 75 and the forked ends 76 by springs 7 9 which are disposed between contact members 69 and the first mentioned legs of said support members. The cross-head 68 is provided with a stud 80 projecting therethrough and having one end threaded to the support members '24. Secur ing nuts 81 on the opposite ends of the studs 80 provide terminals for cables 82 which short-circuit that portion of the resistance between the end of the rheostat adjacent bearing 72 and the cross-head 68. A U- shaped channel 83, (see Figure 5), secured to the panel by flat-headed machine screws, cooperates with a stud 85 secured to the crosshead 68 to prevent rotation of said cross-head and uneven wear of the stationary and brush contacts.

The motor 29 has two fields, 31 for driving the same in a forward direction and 32 for driving it in the reverse direction. As the motor 29 drives the cross-head 68 in a forward direction, i. e. from the end adjacent the bearing 7 2 toward the reduction gear box 62, it causes the short-circuitin of more of the resistances 24, 25 and 26. he motor 29, gear reduction box 62, and screw 71 are so designed that the complete forward travel of the cross-head 68 will consume about the same time that it takes for the field windings of the main motor 11, generator 12 and elevator motor 20 to become heated from cold condition to their maximum temperatures. Limit switches 86 are disposed in the path. of the cross-head 68 to break the power circuit to each of the reversing field windings 31 and 32 by opening one'set of contacts Y5 and thus stop the movement of the crosshead in either direction. 'The cross-head 68 then remains idle until the other field winding is excited causing the movement of the cross-head to the other limit or to an intermediate point if the rheostat motor field windings are again reversed to cause reverse travel of the crosshead. I

In the event that the motor-generator set is shut down after complete forward travel of the cross-heads, which usually takes about four hours of continuous operation,-the rheostat motor is reversed, as previously explained, and if the set is restarted a short time thereafter the cross-head is again reversed to move in a forward direction from a point in its travel at which nearly all of resistance of such value as to prevent dangerous speeds beingobtained if a rheostat brush should at any time fail to make contact.

Thus the short-circuiting of the compensating resistances follows very closelythe heating and cooling of the fieldwindings of the motors and generators and as the resistance of these windings vary with their temperature, there is an inverse variation of the compensating reslstances- The current the compensating resistances.

voltage of the generator.

through the field windings of the motors and generator is therefore maintained constant irrespective of the temperature of the windings and uniform operation of the elevators attained.

The positions of the stop switches 86 may be adjusted so as to .stop the cross-head at more advanced or retarded points relative to 7 To this end the switches are slotted as shown at 87 and fastened to the panel 60 by bolts 88 to allow adjustment of the switches in the direction of travel of the cross-head 68. In this way the compensating resistances may be adjusted to correspond with different cold conditions of the motor and generator field windings which may be due to the seasonal temperatures, ventilation of machine rooms or other factors affecting the initial temperatures of the drive units.

In some direct current drive type installations it will be found, due to such factors as improper ventilation of machine rooms, insufficient capacity of drive units, and the like, that adequate compensation for the changes in resistance of the shunt field windings of the driving motor, generator and elevator motor cannot be. obtained by cutting out resistance from their circuits. In such cases resistances may be added to, rather erator shunt field winding. This cuts down the current flowing through the generator shunt field winding, and weakens the generator field, and enables regulation of the output voltage of the generator so that uniform operation of the elevator motor is obtained. For example the shunt field winding of the driving motor may become so heated that its speed may considerably increase regardless of the resistance cut out by the motor driven rheostat. In such event the resistance added to the circuit of the generator separately excited field winding afi'ords compensation to produce the desired output To this end the connections to the compensating resistance 26 may reversed so that resistance is cut in as the rheostat cross-head travels in a forward direction. In other installations compensating resistances may be electrically connected'to but one shunt field winding, for

instance to the generator shunt field winding,

"previously described by primed characters. The compensating resistances 24: 25 and 26 in the A. C. drive system in series with the field windings 58, i8 and 22 or the exciter, the generator and the elevator motor, respectively. Y designates contacts for limit switches actuated by the crosshcad 68 as in the previously described arrangement. and K designate reversing switch conoacts adapted to operate in connection- "Witi he starting and stopping of the motor-generator set. in this arrangement the speed of the driving motor is subst tially constant, so that as the temperature of the enciter field windings and the generator sepi: .tely excited field windings increases, ance is cut out of both the circuit to the error er field windings and that of the generator field windings. in this Way the generator output voltage may be lrept substantially constant if desired,

As many changes could mad, above described arrangements, and .m parently Widely embodiments of this invention could be made Without departing from the scope thereof, it is intended that all mattercontained in the above description or showing shall be interpreted as illustrative and not in the limiting sense.

What is claimed is:

1. in combination, an elevator car, a hoisting motor therefor, a separately excited field Winding for said motor, a source of current for said field Winding, a resistance electrimeans operable a predetermined rate for varying said resistance in such manner as to cause substantially the same amount of current to be supplied to said "Winding from said source during operation of said motor at a certain speed, regardless of the increase in resistance of said Winding due to current flow therethrough.

2., In combination, an elevator car, a hoist ing motor therefor, a separately excited field winding for said motor, a source of current for said field Winding, resistance connected to said Winding, and means operable at a rate commensurate With the rate of change in the value of the resistance of said Winding incident to the flow and discontinuation of the flow of current therethrough for varying said resistance to maintain a uniform flow of current through said field Winding.

3. In combination, an elevator car, a hoisting motor therefor, a field Winding for said motor, a source of current for said Winding,

' mechanism for connecting and disconnecting said Winding to and from said source, and means operable at a predetermined rate and controlled by said connecting and .disconnecting means for compensating for variations in the value of the resistance of said Cally connected to said field Winding, andwinding caused by temperature changestherein.

thereof incident to the do or discontinue- "ion of the flow of current 1 said Winding 4;. In combination, an poor car, ho ing motor therefor, a separately elicited Winding for said motor, source oi oi tor said motor, means for controlling supply of current from said source to said field Winding, a rheostat in circuit ith sa .3. field Winding, a motor for open ng said rheostat, and mean responsive to said cur 5;: rent controlling mea s for ca the eration of said I'hGOSb g 1 varv the resistance of said. rlieos 5, In combination, elevator car, a hcisting motor therefor, a source of urre a switch torcontrolling the supply of c ore said source to said motor, a I. or controlling the operation of said motor, and me s responsive to the closin of said switch for causin the variation of said re- 3: sistance at predetermined rate and responsive to the opening of said switch for causing the opposite variation of said resistance at a predetermined rate.

6. In combination, an elevator car, driving mechanism for said car, said mechanism com-- prising a dynamoelectric machine having a Winding, a resistance for controlling the amount of current supplied to said Winding,

means for varying said resistance, means for starting and stopping said mechanism, and means dependent on said starting and stopping means for causing the variation oi said resistance by said resistance varying means to be such as to compensate for varia tions in the value of the resistance of said winding incident to the flow and discontinuation of the flow of current therein.

'2'. In combination, an elevator car, driving mechanism for said car, said mechanism. comprising a dynamo-electric machine having a Winding, a resistance for controlling the amount of current to said Winding, means for varying said resistance, and time controlled means for causing the variation of i said resistance by said resistance varying means to be such as to compensate for variations in the value of theresistance of said Winding incident to the amount and duration of the flow of current therein. '11 8. in combination, an elevator car, a hoistmg motor therefor, a Winding for controlling the operation of said motor, control mechanlsm for controlling the amount of current supplied to said Winding, the amount of current flowing through said Winding being dependent upon the operable condition of said control mechanism, and time controlled means for causing the amount of current flowing in said Winding for each operable 1 condition of said control mechanism to be substantially the same, regardless of changes in the resistance of said Winding due to the flow or discontinuation of the flow of current IOU 9. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, means for driving said generator, a separately excited field winding for said motor, a separately excited field winding for-said generator, a source of 7 current for each of said field windings, and

means for causing substantially uniform operation of the elevator car, regardless of variations in the value of the resistance of said field windings incident to the flow and discontinuation of the flow of current there through, said means comprising resistance connected to each of said field windings and time controlled means for varying said resistances.

i 10. In combination, an elevator car, a

hoisting motor therefor, a generator for sup of the flow of current in said field windings.

11. In combination, an elevator car, a hoisting motor therefor, a'generator for supplying current to said motor, means for driving said generator, a separately excited field winding for said ihotor, a separately excited field winding for said generator, a source of current for eachof said field windings, a re sistance in circuit with said generator field winding, a resistance in circuit with said motor field winding, and time controlled means for varying said resistances in such manner as to cause the same current'to be supplied to said motor field winding and the same voltage to be generated by said generator for each operation of the elevator car at full speed, irrespective of variations in the resistance of said field windingsdue totemperatu're changes caused by the flow and discontinuation of the flow of current throughsaid windings.

12. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, driving means for said generator, a separately excited field winding for said motor, a separately excited field winding for said generator, a source of current for each of said field windings, means for starting said driving means inoperation, a rheostat having a plurality of resistances,

' one in circuit with each of said field windings, and means responsive to the starting of sa1d driving means for causing the operation of said rheostat to vary each of said resistances.

o v 1 13. In combinatlon, an elevator car, a

hoisting motor therefor, said hoisting motor having a field winding, a generator for supplying current to said motor, said generator aving a field winding, substantially constant speed driving means for said generator, an exciter driven by said driving means, said exciter having a field winding, a plurality of resistances, one in circuit with each of said field windings, means for causing substantially uniform operation of said elevator car, said last-named means comprising time controlled means for varying each of said resistances in such manner as to compensate for the variations in the value of the resistance of the field winding for which such resistance is provided.

14. In combination, an elevator car, a hoisting motor therefor, said hoisting motor having a field winding, a generator for supplying current to said motor, said generator having a field winding, substantially constant sneed driving means for said generator, an exciter driven by said driving means, said exciter having a field winding, a rheostat having a plurality of resistances, one in circuit with each of said field windings, and means responsive to the starting of said driving means for causing the operation of said rheostat to vary each of said resistances.

15. In combination, an elevator car, a hoisting motor therefor, said hoistin motor havinga field winding, a generator or supplying current to said motor, said generator having a field winding, substantially constant s' eed drivin means for said generator,

an exciter'driven by said driving means, said exciter having a field winding, means for starting and stopping said driving means, a rheostat having a plurality of resistances, one in circuit with each of said fieldwindings, means responsive to the starting of said driving means for causing the operation of said rheostat to vary each of said resistances,

and means responsive to the stoppingof said a driving means for causing the operation of said-rheostat to oppositely vary each of said resistances. o l

16. In combination, an elevator car, a hoisting motor therefor, a generator forsupplying current to said motor, driving means for said generator, a separately excited field winding for said motor,.a separately excited field winding for said gerierator, a-source of .curr-entfor each of said field windings, means for starting said driving means in operation, asrheostat having a plurality of resistances, one in circuit with each of said field windings, means for operating said rheostat at a predetermined rate, means responsive to the starting of said driving means for causing the operation of said rheostat by said operating means in a certain direction to vary each of said resistances, and means for stopping the operation of said rheostat by said operating means after continuous operation thereof in said certain direction for a predetermined time after it has been started in operation. f

17. In combination with an elevator car, an elevator motor, a generator for supplying current to said elevator motor, a driving motor for operating said generator, a separately excited field winding for each of said motors and said generator, a source of current for said field win-dings, means for starting the operation of said driving motor, and means operable in response to the operation of said starting means to compensate for variations in the resistance of the field windings due to heating of the windings incident to the flow of current therein.

18. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, a driving motor for said generator, a separately excited field winding for each of said motors and said generator, a source of current for each of said field windings, a resistance connected to each of said field windings, and time controlled meansfor varying said resistances in such manner as to provide substantially uniform operation of the elevator car, regardless of variations in the resistance of any of said field windings due to the flow or discontinuation of the flow of current therein.

19. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, a driving motor for said generator, a separately excited field winding for each of said motors and said generator, a source of current for each of said field windings, means for starting and stopping said driving motor, a rheostat having a plurality of resistances, one in circuit with each of said field windings, means responsive to the starting of said driving motor for causing the operation of said rheostat to vary each of said resistances, and means responsive to the stopping of said driving motor for causing operation of said rheostat to oppositely vary each of said resist- ZIHCBS.

20. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, a driving motor for said generator, a separately excited field winding for each of said motors and said generator, a source of current for each of said field windings, means for starting andstopping said driving motor, a rheostat having a plurality of resistances, one in circuit with each of said field windings, a motor for operating said rheostat to vary each of said resistances, and means responsive to the starting of said driving motor for causing operation of the rheostat operating motor in one direction to vary each of said resistances and responsive to the stopping of said driving motor for causing theoperation of the mental rheostat operating motor in the opposite direction to oppositely vary each of said resistances.

21. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, means for driving said generator, a separately excited field winding for said motor, a separately excited field winding for said generator, a source of current for each of said field windings, means for starting and stopping said driving means, a rheostat having a plurality of resistances, one in circuit with each of said field windings, means for operating said rheostat, and means responsive to the starting of said driving means for causing the operation of said rheostat by said operating means in a certain direction from a predetermined point to vary each of said resistances and responsive to the stopping of said driving means for causing the operation of said rheostat by said operat ing means to return it to said predetermined point to oppositely vary each of said resistances, said operating means causing operation of said rheostat at the same rate in either direction so that in case the driving means is restarted before the rheostat is returned to said predetermined point, said operating means is caused to reverse the operation of said rheostat at the point to which it has been moved at the time that the restarting of the driving means is effected.

22. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, driving means for said generator, a separately excited field winding for said motor, a separately excited field winding for said generator, a source of current for each of said field windings, means for starting and stopping said driving means, and means for causing substantially uniform operation of said hoisting motor, said lastnamed means comprising a rheostat having a plurality of resistances, one in circuit with each of said field windings, means for operating said rheostat and means responsive to the starting of said driving means for causing the operation of said rheostat by said operating means to vary each of said resistances to compensate-for increases in the value of the resistance of each of said field windings and responsive to the stopping ,of said driving means for causing the operation of said rheostat by said operating means in the opposite direction to oppositely vary each of said resistances to compensate for decreases in the value of the resistances of each of said field windings, said operating means operating said rheostat at the same rate in either direction so as to provide proper compensation for the changes in resistance of said field windings in case of short periods of shut-down of said driving motor.

I 23. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, a driving motor for sald generator, a separately excited field winding for each of said motors and said generator, a source of current for each of said field windings, means for starting and stopping said driving motor, a rheostat having a plurality of resistances, one in circuit with each of said field windings, a motor for operating said rheostat to vary each of said resistances, means responsive to the starting of said driving motor for causing operation of the rheostat operating motor in one direction to vary each of said resistances and responsive to the stopping of said driving motor for causing the operation of the rheostat operating motor in the o posite direction to opposite y vary each 0 said resistances, said rheostat having limiting positions of operation, and means for stopping said rheostat operating motor upon sald rheostat reaching either of said limiting positions.

In testimony whereof, we have signed our names to this s ecification.

LEE IR IN DAVIS.

DAVID CARL LARSON.

GEORGE WILLIAM LAUTRUP 

